SELECTIVE MIXED COUPLING OF CARBOXYLIC ACIDS (I). - ELECTROLYSIS, THERMOLYSIS AND PHOTOLYSIS OF UNSYMMETRICAL DIACYL PEROXIDES WITH ACYCLIC AND CYCLIC ALKYL GROUPS

Article abstract of DOI:10.1016/S0040-4020(01)97194-7

14 unsymmetrical diacyl peroxides (R¹CO2-O2CR² with R¹: undecyl; R²: e.g. methyl, propyl, pentyl, nonyl, 2-methylpropyl, 2-propyl, 2-pentyl, cyclopropyl, cyclobutyl, cyclohexyl) are prepared in 85 to 92 percent yield.Square pulse electrolysis of dodecanoyl octanoyl peroxide (1i) affords the unsymmetrical coupling product octadecane (4) in poor yield and selectivity.Thermolysis or photolysis in solution produces preferentially 4, but also considerable amounts of disproportionation products.At -78 deg C the neat peroxides are photolysed selectively to the mixed dimers.With straight chain and β-branched alkyl groups high yields are obtained (63 - 76 percent), with cycloalkyl groups medium yields (42 - 56 percent), and with α-branched diacyl peroxides moderate yields (20 - 33 percent).A comparison of the mixed Kolbe-electrolysis with the low temperature photolysis of the neat peroxide demonstrates the superiority of the latter method in small scale conversion with regard to yield and selectivity.